The direct introduction of a drug, compound, biologically active peptide or protein into the cells of a patient can have significant therapeutic value. However, this approach also has several drawbacks. Of primary concern is the risk of potential toxicity, particularly at dosages sufficient to produce a biological response to the peptide. From a practical perspective, there is also the problem of the cost associated with isolating and purifying or synthesizing the peptides. Moreover, the clinical impact of the peptides is also limited by their relatively short half-life in vivo, which usually results from their degradation by any proteases present in the target tissue.
For these reasons, introduction of bioactive agents, including proteins, into a patient by delivery of a gene or a cell containing a gene that will express a therapeutic protein in the patient/host is an intriguing alternative to administering the substance. However, to date the principal means for introduction of foreign genetic material into a host has involved the integration of the gene into the host genome by, for example, transforming the host's cells with a viral vector. Direct in vivo gene transfer into postnatal animals has also been reported using DNA encapsulated in liposomes including DNA entrapped in proteoliposomes containing viral envelope receptor proteins.
With respect to delivery systems for genes, means such as viral vectors which introduce the gene into the host's genome can present potential health risks associated with damage to the genetic material in the host cell. Use of cationic liposomes or a biolistic device (i.e., a vaccine "gun" which "shoots" polynucleotides coupled to beads into tissue) to deliver genes in vivo is preparation intensive and, in some cases, requires some experimentation to select proper particle sizes for transmission into target cells. Further, any invasive means of introducing nucleotides (e.g., injection) poses problems of tissue trauma (particularly in long-term therapies) and presents limited access to certain target tissues, such as organs.
Means for non-invasive delivery of pharmaceutical preparations of peptides, such as iontophoresis and other means for transdermal transmission, have the advantage of minimizing tissue trauma. However, it is believed that the bioavailability of peptides following transdermal or mucosal transmission is limited by the relatively high concentration of proteases in these tissues.
Injection of "naked DNA" directly into muscle has also been investigated at length. In 1984, work at the NIH was reported which showed that intrahepatic injection of naked, cloned plasmid DNA for squirrel hepatitis into squirrels produced both viral infection and the formation of antiviral antibodies in the squirrels (Seeger, et al, Proc.Nat'l.Acad.Sci USA, 81:5849-5852, 1984). Several years later, Felgner, et al., reported that they obtained expression of protein from "naked" polynucleotides (i.e., DNA or RNA not associated with liposomes or a viral expression vector) injected into skeletal muscle tissue (Felgner, et al., Science, 247:1465, 1990; see also, PCT application WO 90/11092). Feigner, et al. surmised that muscle cells efficiently take up and express polynucleotides because of the unique structure of muscle tissue, which is comprised of multinucleated cells, sarcoplasmic reticulum and a transverse tubular system which extends deep into the muscle cell.
Today, injection of heterologous nucleic acid into cells of striated muscle is generally considered effective to cause expression of DNA or RNA injected into the cells. Gene transfer by injection into subjects of live cells containing nucleic acids that will express therapeutic genes in vivo is also greatly desired, particularly for treatment sites located within a body cavity that can be reached in a relatively noninvasive manner by the use of a catheter. However, gene transfer by injection of nucleic acid or cells containing therapeutic genes is complicated when the injection site is both remote (i.e., located within a body cavity) and in motion. A particularly difficult target for such therapeutic techniques is a beating heart and associated arterial tissue.
Further, even though the amount of the particular isolated therapeutic genes or cells injected into a patient is small, the costs involved in preparation of such therapeutic substances is high. Therefore, any injectate lost during transfer to the patient, for example, by leakage due to too rapid a transfer, represents a considerable monetary loss.
Accordingly, there is still a need in the art for new and better needles and injection systems or surgical assemblages suitable for microinjection of controlled amounts of therapeutic substances without substantial loss of injectate and without substantial damage to tissue, even upon repeat injections. There is a particular need for needles that are adapted for attachment to various types of catheters for such controlled delivery of therapeutic substances at remote locations within the body.